Assembly for producing offshore electricity comprising a wind turbine

Abstract

An assembly for producing offshore electricity comprising: a wind turbine, and a monopile extending along an axis for fully supporting the wind turbine, the monopile comprising a lower end for penetrating in a seabed, the lower end comprising an outer tube and defining an interior volume. The lower end comprises: an inner tube extending in the interior volume and defining a lower opening, the inner tube and the outer tube defining an annular volume, a closure plate welded on the inner tube and closing the lower opening, and wing plates extending in the annular volume and welded on the inner tube and on the outer tube, the wing plates defining a plurality of compartments extending along the axis and defining lower entries adapted for allowing part of the seabed to enter the compartments.

1 . An assembly for producing offshore electricity comprising:
 a wind turbine, and   a monopile extending along an axis intended to be vertical, and adapted for fully supporting the wind turbine, the monopile comprising a lower end adapted for penetrating in a seabed, the lower end comprising an outer tube centered on the axis and defining an interior volume of the monopile,   the lower end further comprising:
 an inner tube centered on the axis and extending in the interior volume, the inner tube defining a lower opening perpendicular to the axis, and the inner tube and the outer tube defining an annular volume, 
 a closure plate welded on the inner tube and closing the lower opening, and 
 a plurality of wing plates extending in the annular volume and welded on the inner tube and on the outer tube, the wing plates defining a plurality of compartments in the annular volume, the compartments respectively extending along the axis and defining lower entries adapted for allowing part of the seabed to enter the compartments. 
   
     
     
         2 . The assembly according to  claim 1 , wherein the wing plates respectfully extend in radial planes with respect to the axis and are regularly distributed around the axis. 
     
     
         3 . The assembly according to  claim 1 , wherein said plurality of wing plates consists of a number of wing plates ranging from four to eight. 
     
     
         4 . The assembly according to  claim 1 , wherein each of the wing plates comprises a lowermost edge and an uppermost edge both connecting the outer tube to the inner tube, the lowermost edge and the uppermost edge being inclined with respect to the axis, and getting lower towards the inner tube. 
     
     
         5 . The assembly according to any  claim 1 , wherein the outer tube has a radial thickness, the wing plates having a thickness comprised between 40% and 60% of the radial thickness Ely of the outer tube. 
     
     
         6 . The assembly according to  claim 1 , wherein the inner tube has an outside diameter and the outer tube has an outside diameter, the outside diameter of the inner tube being comprised between 25% and 75% of the outside diameter of the outer tube. 
     
     
         7 . The assembly according to  claim 6 , wherein the inner tube has an axial extension which is smaller than the outside diameter of the outer tube. 
     
     
         8 . The assembly according to  claim 1 , wherein the closure plate has a circular shape. 
     
     
         9 . The assembly according to  claim 1 , wherein the inner tube defines an inner volume, the lower end further comprising stiffening elements located in the inner volume and adapted for stiffening the closing plate with respect to compression along the axis and bending. 
     
     
         10 . The assembly according to  claim 9 , wherein the stiffening elements comprise plates extending throughout the inner volume and forming a grid in axial view. 
     
     
         11 . The assembly according to  claim 1 , wherein the inner tube, the outer tube, the wing plates and the closure plate comprise steel having a yield strength larger than 355 MPa. 
     
     
         12 . The assembly according to  claim 1 , further including a subsea jacket comprising:
 a structure adapted for being anchored in the seabed and surrounding the monopile around the axis, and   a central guide fixed on the structure and surrounding the monopile around the axis while being vertically free with respect to the monopile, the structure being adapted for resisting horizontal loads applied by the monopile on the central guide due to bending movements of the monopile.   
     
     
         13 . The assembly according to  claim 12 , wherein the jacket further comprises a lower central guide fixed on the structure and surrounding the monopile around the axis while being vertically free with respect to the monopile, the structure being adapted for resisting horizontal loads applied by the monopile on the lower central guide. 
     
     
         14 . The assembly according to  claim 12 , wherein the central guide comprises:
 a ring surrounding the monopile with clearance, and   a plurality of friction pads located between the ring and the monopile and angularly distributed around the axis.   
     
     
         15 . A process for building an assembly according to  claim 1 , comprising the following steps:
 obtaining the outer tube and the inner tube,   positioning the inner tube in the interior volume defined by the outer tube, the outer tube being horizontal, and the inner tube being centered on the axis, and   welding the wing plates on the inner tube and on the outer tube, and welding the closure plate on the inner tube.